I already had a custom part attached to blog posts. After your tip, I called BuildDisplay in Display method of that part's driver and added the result to the returned shape. First I wanted to return a CombinedResult but couldn't figure out how to do that with
BuildDisplay. Then I added the result as a dynamic property to the shape. I think returning a combined result of shapes would be better, So I wouldn't have a Model.Display call in my view, but later maybe.